Myopic little men in tuxedos, or highly efficient land/water
animals? Recent research indicates there’s more to penguins than
meets the eye.
If you’ve every wondered what it would be like to be able to see
as clearly under water as you can on land, just ask the nearest
penguin.Most aquatic animals are short-sighted on land. Most
terrestrial animals (and that includes us) are far-sighted under
water. But researchers have discovered that penguins can
apparently see equally well in both environments, because of the
unique structure of their eyes.
Penguins have to be able to see well under water because their
diet consists mainly of plankton, molluscs, crustaceans, and the
inevitable fish. Through a special slowing-down of their heart
rate they’re able, like many other diving animals, to stay
submerged long enough to search out and chase whatever catches
their fancy.
On dry land, it’s a different story-or has been up to now.
Waddling along on their flat little feet, eyes fixed intently on
the ground, penguins appear myopic, inefficient and generally out
of place.
In fact the reverse is true. During a recent stay on the
Falkland Islands, a Canadian researcher discovered that penguins
are able to recognize individuals and navigate the rocky terrain
on which they live quite well. Long of body and short of
leg, they probably poke their heads forward as an aid to balance.
And as for looking at the ground, they’re merely-like us-keeping
an eye on where they’re going.
The human eye is adapted for aerial vision, which is why scuba
divers-or even you and I in the local swimming pool-must wear
goggles or a face mask to re-introduce air in front of our eyes
in order to see clearly.
Among vertebrates in general, the bird eye is frequently
described as the most efficient. Its superior quality, combined
with the fact that a large number of birds-cormorants, pelicans,
seagulls, even ducks, as well as penguins-get their food from
water, obviously deserved research beyond that possible in a
controlled environment such as an aquarium or zoo. Professor
Jacob Sivak of the University of Waterloo and his associate,
Professor Howard Howland of Cornell University, had a chance
to do that research recently. Their trip had but one purpose-to
study the structure of penguins’ eyes while observing their
natural habitat.
The Falkland Islands, off the coast of Argentina, offered this
opportunity, being one the few areas outside Antarctica where
penguins can be found in large numbers. Three of the 16 known
species were located there: the Gentoo, which live on flat
areas right off the beach; the Magellan (also called Jackass),
which live in burrows; and the Rock-hoppers, which live among the
rocks along the cliffs.
The Rock-hoppers were by far the most common, having a population
of well over 100,000. The general rule is, the smaller the
penguin, the meaner the temperament, and the researchers did
witness the odd fight. Their flippers may look pretty useless
out of water, but it’s not smart to play around with a penguin.
Hel’ll stand his ground in a face-off and if you’re foolish
enough to get too close, those flippers can knock you
flat.
Dr. Sivak and his associate, however, had little trouble. Rock-
hoppers always congregate in fairly tight groups, as a defense
against predatory birds such as the skua (a large seagull that
thinks it’s a hawk), and two more upright figures in their
midst didn’t seem to bother them.
Standing as close to their subjects as 0.3m, the scientists used
two devices: one, developed by Professor Howland, to take
photographs of the penguins’ eyes; the othger, developed by Dr.
Sivak, to shine a series of concentric circles on the cornea and
give a measurement of how reflections of objects are altered by
curvature of the eye.
Despite the fact all the work had to be done at night-the only
time the penguins’ pupils were dilated enough-the results were
worth it. Comparison of the photographs with similar photos
of human eyes, and study of the internal structure of the eyes of
creatures discovered killed by seal lions, proved the scientists’
theory that the penguin’s eyes are the secret of its survival.
In general terms, a penguin eye and a human eye are almost
identical. Both have the same components necessary for vision-a
cornea through which light can enter; an iris which controls the
amount of light that enters; and a crystalline lens that focuses
the light onto the back of the eye where a specialized membrane,
the retina, receives it and passes the message along the optic
nerve to the brain for interpretation.
In the penguin eye, hoever, there are many subtle differences.
The cornea, for example, is markedly flattened compared to ours –
– so much so that it almost resembles a window-pane. This
greatly alters the angle at which light can enter the eye
and is very important for underwater swimming, when light enters
the eye obliquely through a medium (water) whose density is quite
different to the density of air.
The penguin iris is controlled by a very powerful muscle which is
able to drastically alter the shape of the lens attached to it,
depending on whether the penguin is in or out of the water. The
lens, comparatively larger than ours and differently shaped,
focuses the light coming through the flattened cornea onto the
retinal body at the back of the eye. In this way, the penguin
eye adapts to whatever medium it happens to be in at the time.
Interestingly, there was no evidence of eye problems (apart from
one incident of blindness due to injury) in the group of penguins
studied. Of course penguins don’t read, watch TV or encounter
any of the numerous irritants we land-bound animals subject
ourselves-or are subjected-to during our lifetime.
Both the testing devices and methods used in this study are
easily adaptable for use with human eyes, paving the way for
fast, easy identification of eye problems. Also, the researchers
hope that the insights they’ve gained into how animals deal with
two environments may lead to knowledge of how humans, in the
future, might do likewise.
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PENGUINS (C) 1987 Ontario Science Centre.
May be duplicated for use on other information
services with permission.
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